Thin-film temperature sensor.

Abstract

A new device has been developed for sensing small and rapid temperature changes accompanying biochemical reactions. The active element consists of an evaporated thin-film capacitor having a relatively strong temperature dependence. This dependence is derived from electron trapping effects in the thin amorphous dielectric film. A voltage output of at least 50 mV/deg can be obtained prior to amplification by using a resonant ac bridge circuit operating at 100 kHz. The corresponding noise output for a 10 kHz bandwidth can with an optimum circuit be as low as 4 microvolts. Therefore, the minimum detectable temperature change would be 80 microdegrees at 10 kHz. Rapid thermal response is assured by supporting the thin-film capacitor on a thin anodic tantalum oxide film suspended across an electrolytically etched window in a tantalum foil.